The Panel Experiment

	Introduction			Interconnections
	Experimental Layout			Results
	Panel Assembly

Introduction:

After the completion of three prototype rangefinders it was decided to implement a full scale test and demonstration of the active surface together with the metrology system a 150 foot high tower is conveniently located close to the interferometer building in Green Bank and a rangefinder was installed approximately 100 feet up this tower and together with the two rangefinders on the ground, the initial proposed geometry for the surface surveying of the GBT was duplicated. The rangefinders were arranged so that they could measure to a test panel assembly representing the outermost edge of the GBT surface.  The assembly consisted of nine full size surface panels mounted on a frame via nine linear actuators in the manner proposed for the active surface of the GBT. Nine retroreflectors were mounted above the actuators on the surface. The frame could be moved by a separate actuator so simulating movements of the surface that could be sensed by the metrology system and, if the system worked, corrections would be applied by moving the panel actuators.

The rangefinders were interfaced to a controlling computer located in the basement of the interferometer building. This was, in turn connected to a computer controlling the actuators thereby completing a system very similar to the one proposed for the GBT.

The Results:

The panel experiment yielded excellent results. One surprise was the stability of the tower involved. This is shown in the Figure 1 in which the range was measured from the rangefinder tower to a point on the ground for a period of approximately 2 hours. As may be seen, the fluctuations in the recorded range are small--an RMS of 58 µm with an integration period of 128 milliseconds.

The rangefinder on the tower was used to measure controlled movements of an actuator on the panel assembly. The commanded movements of the actuator and the movements measured by the rangefinder were in excellent agreement and some idea of the quality of the data may be inferred by Figure 2.

Finally, the system was used to correct a disturbance injected by the single actuator and at the 5-10 µm level, the correction seems to be complete.

Comments or Problems:

• Please direct any comments regarding content to John Payne, jpayne@nrao.edu
• Regarding matters of style, please direct all comments to Ramón E. Creager, rcreager@nrao.edu.
  

This page was last modified on September 11, 1997.

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